There are known hearing aid circuits which provide frequency shifting of analog signals in a real time manner for reducing the frequency of such signals for a person having limited frequency audibility. Examples of such circuits are found in U.S. Pat. No. 4,271,331 to Kalkstein, U.S. Pat. No. 4,366,349 to Adelman and U.S. Pat. No. 4,419,544 to Adelman. Typically the frequency shifting is produced by using a multi-element storage component such as a conventional serial analog delay element. The signal moves through each serial memory in a "bucket brigade" fashion in response to clock pulses. The timing of the clock pulses is varied in order to achieve desired delays and frequency shifts.
The above technique has a significant disadvantage. Due to the fact that frequency reduction is produced by setting the clocking-out rate from the delay element to be slower than the clocking-in rate thereto, there is necessarily a loss of information which is related to the amount of frequency reduction. This loss of information arises due to the fact that more information is being supplied to the delay element than is being read out therefrom.